1. Field of the Invention
This invention relates generally to data communication systems and more particulary to digital apparatus and method for a carrier data operated squelch.
2. Description of the Prior Art
Phase shift keyed (PSK) modulation techniques are widely used in digital signalling over RF communication channels. In digital phase shift keying, digital information is communicated over the channel by sequentially transmitting carrier pulses of constant amplitude, angular frequency and duration but of different relative phase. Demodulation of PSK signals is accomplished by detecting the relative phase of the incoming signal and using the phase information obtained to determine the data content of the modulated signal. Present PSK demodulator systems generally employ hybrid arrangements of digital and analogue circuit components. Such PSK demodulators generally require on-site calibration and periodic readjustment.
Many of these problems can be solved by utilizing a digital sampling board phase locked loop method for PSK demodulation and detection. With such systems it is often desirable to provide squelch capability based upon carrier data detection to permit audio muting or data steering functions. Prior art circuits for carrier detection required complex circuitry with fixed parameters and were unduly expensive to manufacture.